Doing a dump of a data structure containing some Math::BigRat numers, one of them came out as:

Math::BigRat->new(15715642....00000)

What was the output you wanted/expected to see ?

When I eval (or do) this file (with Math::BigRat loaded of course), it fails silently. When I remove this line, it succeeds.

That's not a very meaningful description of what happens(to me, at least). Better if you could post a minimal script that demonstrates the problem.

Cheers,
Rob